Planographic printing plate and processes



Sept. 27, 1966 D. A. NEWMAN PLANOGRAPHIC PRINTING PLATE AND PROCESSES Filed June 13, 1962 20 Foa/VD@ 7mo/U INVENTOR.

United States Patent O 3,274,929 PLANOGRAPHIC PRINTING PLATE AND PROCESSES Douglas A. Newman, Glen Cove, N.Y., assigner to Columbia Ribbon and Carbon Manufacturing Co., lne.,

Glen Cove, N.Y., a corporation of New York Filed June 13, 1962, Ser. No. 202,188

4 Claims. (Cl. lill-149.2)

This invention relates to the art of producing duplicate copies of an imaged original sheet by thermographic means, and more particularly to novel heat-self-imaging planographic printing plates which may be thermographically imaged, and to the method of making the same.

It has been known for .some time that duplicate copies of an imaged original sheet may be formed by means of infrared radiation and a heat-sensitive transfer sheet or copy sheet. The radiation is selectively absorbed by the images on the original sheet land converted to heat. The image heat pattern is conducted to a transfer sheet to cause the transfer layer to melt and transfer in areas corresponding to the imaged areas of the original, or is conducted to a copy sheet coated with heat-reactive chemicals to cause the chemicals to r-eact and form colored image areas in locations corresponding to the imaged areas of the original.

It is also known to image planographic printing plates by the aforementioned transfer method whereby the transfer layer is based upon oleophilic materials and forms oleophilic ink-receptive images `on the hydrophilic printing surface of a planographic plate. Such method has the disadvantages that it requires the use of a special oleophilic transfer sheet in addition to the printing plate and requires the use of special precautions in handling the oleophilic transfer layer in contact with the hydrophilic plate surface and subjecting the same to the radiation. Even the slightest unintentional pressure during handling may result in 4a smudging or smearing of the oleophilic material onto the plate surface and although such may not be noticeable to the eye it renders the plate ink-receptive in unintended areas and the printed copies are heavily inked in these areas and thus useless.

It is also known to produce heat-self-irnaging planographic printing plates thereby avoiding the necessity of using la separate oleophilic transfer sheet but such plates also have the aforementioned disadvantage that they are sensitive to being imaged in unintended areas by the application of pressure. Thus when the plate is handled during superposition with the imaged original sheet or while aligning the sheets for treatment with infrared radiation, care must be taken to avoid pressing the self-imaging plate or it will become ink-receptive in unintended areas and the copies printed therewith will be badly stained or inked in unintended areas. For the the same reason, such pressure-sensitive plates present problems when used in infrared-radiation devices containing pressure rollers, or when stacked in large numbers whereby the plates at the bottom are under pressure due to the weight of pilates stacked on top thereof.

It is an object of the present invention to prepare heatself-imaging planographic printing plates which .are substantially non-pressure-sensitive and which may be conveniently imaged by superposing them with an imaged original sheet and subjecting them to infrared radiation.

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It is another object of the invention to prepare planographic printing plates having a hydrophilic printing coating which is resistant to pressure but which may be rendered oleophilic by merely heating the same.

It is still another object of the invention to apply a thin, even, uniform hydrophilic printing coating over a heat-rneltable oleophilic coating on the surface of a planographic printing plate.

These and other objects and advantages are accomplished as will be obvious to those skilled in the art in the light of the present specification and drawing in which:

FIGURE l is a diagrammatic cross-section, to an enlarged scale, of an imaged original sheet and a heat-selfimaging planographic printing plate superposed under the influence of infrared radiation but spaced for purposes of illustration.

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of a heat-imaged planographic printing plate prepared and imaged according to the present invention.

The heat-self-imaging planographic printing plates of this invention comprise a suitable flexible foundation 20, preferably wet strength paper as conventionally used in the planographic plate art. The foundation has thereon a heat-meltable oleophilic coating or layer 21 which is applied as an aqueous suspension or emulsion and dried to form a layer having a rough surface. Finally a thin hydrophilic coating or layer 22 of conventional planographic printing material is applied over the oleophilic layer and dried to form the heat-self-imaging plate.

When the plate is heated in selected areas, preferably by means of infrared radiation in the manner illustrated by FIG. l of the drawing, the oleophilic layer melts and flows into or is absorbed by the hydrophilic top coating in the heated areas and renders the same oleophilic.

According to the invention it has been found essential that the oleophilic layer have a rough uneven surface so as to provide tooth or holding power for the hydrophilic printing coating. As is obvious to those skilled in the art, ol-eophilic materials repel hydrophilic materials and thus it has been found necessary when applying :the thin hydrophilic coating to the highly -oleophilic layer that the latter have a rough uneven surface. In this connection excellent results are obtained by applying the oleophilic layer from an aqueous wax emulsion or dispersion whereby the wax is present in the form of insoluble particles and is deposited on the foundation as a layer made up of such wax particles. Thus the layer has a rough uneven surface which provides good receptivity and tooth for the hydrophilic coating `as opposed to wax layers applied by hot melt techniques land having smooth surfaces.

Most suitable are oleophilic layers based upon hard wax such as carnauba wax, rouricury wax, Be Square wax, montan wax 'and the like, as well as mixtures thereof, since these waxes provide increased resistance to pressure displacement. However, other conventional natural and synthetic waxes may also be used provided that they are not water-soluble and provided that, in the case of the softer waxes, they be applied as relatively thin layers or in admixture with one or more of the aforementioned hard waxes.

-ln preparing the wax emulsion, the wax is emulsi-ed in a major amount of water with the aid of a conventional emulsifying agent such as a mixture of a fatty acid and an alkali.

The following example is illustrative of a suitable water-borne wax emulsion and its application to a plate foundation to form a heat-meltable oleophilic layer:

Example 1 Parts by Ingredients: weight Ouricury wax 4 Be Square wax (petroleum wax) 4 Oleic acid 6 Potassium hydroxide `8 Water 10 The above ingredients are blended together and agitated to rform a uniform emulsion with the aid of the p-otassium oleate soap emulsifying agent. Agitation is continued until the waxes are uniformly suspended in minute particulate form and the composition attains a smooth coatable consistency. The composition is then coated onto a wet strength paper foundation and the water is evaporated to deposit the discrete wax particles in the form of a colorless heat-meltable oleophilic layer having a rough, porous surface having a good receptivity or holding power for the planographic printing surface coat.

There is no particular critically with respect to the selection of the printing coat, and any of the known hydrophilic colloid and the like binder materials conventionally used in the planographic printing plate art are suitable, such materials including for instance polyvinyl alcohol, carboxymethyl cellulose, casein, gelatin, sodium alginate and the like.

It is essential that the planographic coating contain an amount of ller and it has been found that the amount of filler used, such as clay, attapulgite, talc, blanc fixe, titaniurn oxide and the like, should be increased as the thickness of the planographic coating is increased. Thus, for coatings having a thickness of 2 points, the ratio of filler to binder should range from between to l and 7 to 1. With planographic coatings having a thickness of 1 point, the ratio should range between 4 to 1 and 6 to 1 while a range between 3 to 1 and 5 to 1 is preferred with coatings having a thickness of 0.5 point.

The planographic coating is preferably insolubilized in known manner by either incorporating a salt, aldehyde, or the like curing agent into the printing coating to render it self-insolubilizing or by applying the curing agent to the applied printing coating as a wash to accomplish insolubilization.

It is preferred to apply the planographic coating as a thinner or lighter weight coating than is conventional in the art. Thus, although coatings having a conventional weight of 8 or more pounds per ream may be successfully used by increasing the thickness and heat-ilowability of the underlying oleophilic layer, it is preferred to limit the weight of the planographic coating to the order of from about 1 to about 6 pounds per ream.

The following example is illustrative of a planographic printing coat composition used according to the invention:

Example 2 Parts by Ingredients: weight Sodium carboxymethyl cellulose gms 2 5% ammoniacal copper sulfate cc 40 Chromium trioxide gms 0.5 Ferric ammonium citrate gm 1.0 Water cc -90 Clay gms 8 The above ingredients including the salt insolubilizing agents are mixed to a coata-ble consistency and applied over the oleophilic coating on the foundation coated according to Example 1 and dried to evaporate t-he water and ammonia to form an insolubilized planographic printing coating having a weight of about 3 pounds per ream.

The hydrophilic printing coat adheres very well to the heat-meltable oleophilic coating, apparently due to an integration of the planographic coating into the pores and rough surface areas of the oleophilic coating. However the printing coating has a relatively smooth surface and is present as a thin uniform hydrophilic layer which masks the oleophilic properties of the heat-meltable layer,

T he formed plate may be handled, struck with a blow from a type bar or stored for extended periods of time under weight pressures without any inadvertent interference with the hydrophilic properties of the printing coating.

When it is desired to heat-image the plates of this invention, this may be accomplished directly by means of a heated stylus, heated type bars or other heated body, or preferably indirectly by means of radiated heat as illustrated by the drawing.

Thus the plate comprising the foundation 20, the oleophilic coating 21 and the hydrophilic coating 23 is superposed with an original sheet such as a paper sheet 10 having thereon infrared radiation-absorbing images 11 as shown by FIG. l and subjected to a light source 50 which emits radiation rich in the infrared range. This may be accomplished by passing the superposed sheets through a Thermo-Fax machine, or by means of a conventional flat bed type infrared apparatus.

The radiation is selectively absorbed by the original images and converted to heat while the unimaged areas of the original sheet either reflect the radiation or allow it to pass through unabsorbed. The heat generated by the original images is conducted to the plate where it melts corresponding areas of only the oleophilic coating and causes them to How into or be absorbed by the solid hydrophilic printing coating rendering the same oleophilic in areas 2S corresponding to the imaged areas of the original sheet as illustrated by FIG. 2.

This effect is attained mainly because of the porous nature of solid planographic printing coatings containing absorbent ller materials. The melted oleophilic material penetrates through the solid planographic coating to render the surface thereof oleophilic in the heated areas.

As is obvious to those skilled in the art, in the light of the present description, the weight and thickness of the oleophilic and hydrophilic coatings may be varied depending upon the ilowability of the oleophilic materials used and the porosity of the planographic coating.

It is generally preferred Ithat the oleophilic layer be deposited so as to have an average thickness of from 3 to 5 points, a point being equal to 0.0001 inch, and that it be -so constituted as to have a melting point in the range of from to 200 F. The thickness of the oleophilic layer is directly proportional to the weight of the planographic coating, thinner planographic coatings requiring thinner oleophilic undercoatings to effect the desired results.

The imaged plates of this invention are used in conventional manner in the planographic printing process for the production of several hundred copies which correspond exactly with the imaged original sheet.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. The method of producing a heat-imageable planographic printing plate which 4comprises applying to a flexible foundation sheet an aqueous wax emulsion composition comprising discrete, minute particles of wax, an emulsifying -agent and water, evapora-ting the water to form a heat-meltable oleophilic l-ayer of discrete, minu-te wax particles, said layer having a thickness within the range of 3 to 5 points, a melting temperature within the -r-ange of 120 F. to 200 F. and having a rough uneven surface providing good reciptivity for a hydrophilic printing coating, applying over said layer a water-insoluble hydrophilic printing composition comprising 1 part by weight of a hydrophilic binder material, from 3 to 7 parts by weight of an absorbent filler 'and water and evaporating the water to form a hydrophilic printing coating having a thickness of from 0.5 to 2 points which is capable of remaining solid at temperatures below 200 F. and being penetrated and rendered oleophilic by said oleophilic layer when the latter is heated to a temperature between 120 F. and 200 F. to reduce it to fluid condition, said oloephilic layer not being capable of rendering Isaid printing coating oleophilic under the effects of imaging pressure.

2. A heat-imageable .planographic printing plate com- .prising a flexible foundation sheet having on the surface thereof a heat-meltable oleophilic layer comprising the residue of an aqueous Wax emulsion comprising discrete, minute particles of wax, an emulsifying agent and water after the evaporation of said water, said layer having a thickness Within the range of from 3 Ito 5 points, a melting temperature within the range of from 120 F. to 200 F. and having a rough uneven surface providing good receptivity for a hydrophilic printing coating, and having on said rough Iuneven surface -a water-insoluble hydrophilic printing coating comprising 1 part by weight of a hydrophilic binder material and from 3 to 7 parts by weight of an absorbent filler and having a thickness of from 0.5 to 2 points and which is capable of remaining solid and being penetrated and rendered oleophilic by said oleophilic layer when the plate is heated to a temperature Within the range of 120 F. to 200 F., said oleophilic layer not being capable of rendering said printing coating oleophilic under the effects of imaging pressure.

3. A heat-imageable planographic printing plate according to claim 2 in which the foundation sheet, the oleophilic layer and the hydrophilic printing coating are substantially free of materials which absorb infrared radiation.

4. The method of ima-ging the planographic printing plate of claim 3 which comprises superposing said plate together with an original sheet having thereon images comprising infrared radiation-absorbing heat-generating material, said original sheet being in surface contact With the hydrophilic printing coating lof said plate, `and subjecting the original sheet to a radi-ation source rich in infrared whereby the heat gener-ated by the original images heats corresponding areas of the plate and causes the oleophilic layer to melt and render the hydrophilic coating oleophilic and ink-receptive `in said corresponding areas.

References Cited bythe Examiner UNITED STATES PATENTS 1,245,120 10/1917 Neidich lOl-149.2 2,663,657 12/1953 Miller et al. 2,800,077 7/1957 Marron 10l-149.2 2,967,785 1/1961 Allen et al. 250-65 X DAVID KLEIN, Primary Examiner.

ROBERT E. PULFREY, WILLIAM B. PENN,

Examiners. 

2. A HEAT-IMAGEABLE PLANOGRAPHIC PRINTING PLATE COMPPRISING A FLEXIBLE FOUNDATION SHEET HAVING ON THE SURFACE THEREOF A HEAT-MELTABLE OLEOPHILIC LAYER COMPRISING THE RESIDUE OF AN AQUEOUS WAX EMULSION COMPRISING DISCRETE, MINUTE PARTICLES OF WAX, AN EMULSIFYING AGENT AND WATER AFTER THE EVAPORATION OF SAID WATER, SAID LAYER HAVING A THICKNESS WITHIN THE RANGE OF FROM 3 TO 5 POINTS, A MELTING TEMPERATURE WITHIN THE RANGE OF FROM 120*F. TO 200* F. AND HAVING A ROUGH UNEVEN SURFACE PROVIDING GOOD RECEPTIVITY FOR A HYDROPHILIC PRINTING COATING, AND HAVING ON SAID ROUGH UNEVEN SURFACE A WATER-INSOLUBLE HYDRO- 